Electron beam deflection system



March 14, 1961 E. GUNDERT ETAI.

ELECTRON BEAM DEF'LECTION SYSTEM 2 Sheets-Sheet 1 Filed May 22, 1957 men! mwomnom JOmPZOO mozmomm zoo QrPuZw 20mkouJu INVENTORS 2 EBERHARD GUNDERT,

GERWIG VIBRANS Y I THEI TTOR EY.

March 14, 1961 E. GUNDERT ET AL 2,975,325

ELECTRON BEAM DEFLECTION SYSTEM Filed May 22, 1957 2 Sheets-Sheet 2 ELECTROSTATIC CONVERGENCE CONTROL SOURCE STATIC STATIC 60w AND AND DYNAMIC DYNAMIC ELECTROMAGNETIC CONVERGENCE CONTROL SOURCES INVENTORS. EBERHARD GUNDERT,

GERWIG VIBRANS BY Mm THEI ATTORNEY.

2,975,325 Patented Mar. 14, 1961 ELECTRON BEAM DEFLECTION SYSTEM Eberhard Gundert, Ulm (Danube), and Gerwig Vihrans, I Braunschweig, Germany, assignors to General Electric Company, a corporation of New York Filed May 22, 1957, Ser. No. 660,885

Claims priority, application Germany May 26, 1956 .4jcla mss (Cl. 31522) 1 n This invention relates to electron discharge devices employing electron beams, and more particularly to improved means for effecting deflection of a plurality of electron beams therein.

One type of plural electron beam electron discharge device to which the present invention is particularly applicable is a cathode ray tube having three electron beams, and useful for example as a picture display device for color television. The purpose of the three electron beams in such a cathode ray tube is to excite different respective components of the screen of the tube. For good image resolution and proper color fidelity the three electron beams must be converged to meet at a common point. To enable the three electron beams to be properly converged a deflection system has already been proposed in which each of the two outer electron beams passes between a pair of deflection plates between which are produced both magnetic and electrostatic deflection fields. The deflection plates are so mounted that the magnetic fields produced between the plates deflect the electron beam in a plane parallel to the desired plane of convergence. Such an arrangement is described and claimed in the co-pending application of Paul H. Gleichauf, Serial No. 565,859, filed February 16, 1956, now Patent 2,907,915 and assigned to the assignee of the instant application. The present invention provides an improvement over the deflection system described and claimed in the aforesaid co-pending application.

A principal object of the present invention is to provide an improved electron beam deflection system for an electron discharge device of the multiple electron beam type.

Another object is to provide an improved combined electromagnetic and electrostatic electron beam deflection system for a plural electron beam cathode ray tube.

Still another object of the invention is to provide an improved electron beam convergence arrangement for cathode ray tubes and the like which is mechanically simple and relatively inexpensive to manufacture, and which provides improved control of the electron beams with a minimum of control equipment.

Another object of the present invention is to provide, r

in a color television picture tube of the type employing three co-planar electron beams, means for effecting static and dynamic convergence of the electron beams.

These and other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawing, and the scope of the invention will be defined in the appended claims.

Briefly in accordance with the present invention we provide, in conjunction with each electron beam to be converged, a pair of mutually angularly related magnetic deflection plates and a separatepair of electrostatic deflection plates substantially coincident with the magnetic plates. A magnetic field is formed between the magnetic plates with a polarity such as to deflect the electron beam in a desired direction, and the plates are disposed in such angular relation to one another as to make the intensity of the magnetic field substantially uniform throughout the space between them. This provides maximum linearity of magnetic beam deflection and minimum electron beam distortion. For corresponding uniformity of electrostatic deflection, the electrostatic deflection plates are made of nonmagnetic material and disposed in parallel relation between the magnetic plates. Thus a uniform magnetic and a uniform electrostatic deflection field is formed in which the electron beam will be independently deflected with optimum uniformity in mutually perpendicular directions.

In the drawings: 7

Figure 1 is a schematic fragmentary view of one embodiment of a multiple electron beam cathode ray tube constructed in accordance with the present invention;

Figure 2 is an enlarged semi-schematic illustration of a portion of the structure shown in Figure l, the view being taken in a transverse sectional plane 22 through the neck of the tube of Figure 1.

Referring to Figure 1 there is shown a color cathode ray tube including an envelope 2 having a cylindrical neck portion 4, a transparent viewing end or face plate portion 6, and a substantially conical transitional portion 5.

Located at the viewing end of the envelope 2 is a screen 8 including a layer of phosphorescent material coated on the inner surface of the face plate portion 6. The screen shown is capable of producing light of different colors in response to impingement of electrons thereon and may comprise, for example, a succession of triads of substantially parallel red, green and blue light-producing phosphor stripes, the stripes of one triad being shown to an exaggerated scale in Figure 1 and denoted R, G and B. The screen may also include a layer of conducting material 10 superimposed on the phosphor layer, to which a suitable electron beam accelerating potential may be applied from a suitable bias source, not shown.

In the neck of the tube is mounted a plurality of electron guns 12, here shown as three in number, arranged in coplanar relation. The electron beams from the three guns are shown at 14, 16 and 18. The plane of the electron guns is preferably substantially perpendicular to the phosphor stripes of the screen 8. The three electron guns 12 are suitably connected through an insulative tube base 20 to sources of suitable bias potentials, not shown, and a suitable video signal source generally designated 22. By means of horizontal and vertical deflection coils schematically illustrated and designated 24 and 26 respectively, the electron beams eminating from the electron guns 12 are deflected in both horizontal and vertical planes of deflection, thereby to scan a raster on the screen 8. Spaced from the screen 8 is a substantially concentric electron permeable mask or grid 28, here shown as a grille of fine wires arranged substantially parallel to the phosphor lines and uniformly spaced to provide one interwire space corresponding to each phosphor line triad. Preferably the grille 28 is maintained by a suitable power supply (not shown) at a potential substantially below the potential of screen 8 so that there is a substantial electric accelerating and focusing field between the grille and screen. The three electron beams converge at the locus of the grille 23, and the grille wires are so spaced and positioned with respect to the center of deflection of each electron beam that the beam from each gun impinges only the phosphor stripes of the particular primary color for which it is intended. Thus in accordance with color intelligence received from video signal source 22 the three electron beams form the desired polychrome image on screen 8.

To efliect convergence of the three electron beams in accordance with the present invention we provide in con- .namic misconvergence.

junction with each of the beams to be converged, i.e. each outer beam 14, 18 in Figure 1, a pair of magnetic pole pieces or deflection plates 40 and a pair of electrostatic deflection plates 42. T he magnetic deflection plates 40 are made of ferromagnetic material and are disposed generally parallel to the electron beam and so located that the beam passes between them, The magnetic plates 40 may be mounted on any suitable supporting struct'ure. Preferably plates 40 are maintained at the same potential as the final electrodes of the electron guns, and therefore plates 40 may conveniently be mounted on transverse plate 44, Which is apertured as at 46 to pass the electron beams and may be common with the final element of the electron beam accelerating and focus means of the electron guns 12. A suitable magnetic field between the magnetic plates 49 is induced by a source ofmagnetomotive force in the form of an electromagnet 50 located outside the tube neck and having poles 52 spaced closely adjacent the neck opposite the magnetic plates. To enhance the magnetic coupling between the plates 40"and the magnet 50 the plates are provided with pole-pieces in the form of integral flanges 54 outstanding from their outer edges adjacent to and conforming substantially in curvature with the inside wall of the tube neck.

In accordance with the invention the plates 40 are inclined or angularly disposed relative to one another so that their inside edges 56 are more closely spaced than their edges adjacent the wall of the tube neck. The relative angular disposition of the platesdi) of each pair is made such that when the plates are magnetically coupled through flanges 54 to the magnet the magnetic field between the plates will be substantially uniform throughout the space between the plates. The disposition of the plates 40 is preferably substantially such that the plane of the three electron guns i2 bisects the angle of intersection of the plates. The magnetic field between the plates thus provides deflection of the electron beam .in the plane of the electron guns. The solenoid 58 of the :e'lectromagnet 5,0 is energized from a suitable potential source through an electromagnetic convergence control 60. Each control 60 is preferably adapted for energizing the solenoid of the related magnet 5! with currents suit- .able for correcting both static misconvergence and dynamicmisconvergence, i.e. misconvergence encountered as a result of scanning. That ,is, each control may beadapted for energizing the related solenoid with a direct current of magnitude adjustable to correct for static misconvergence and additionally an alternating current signal of predetermined wave form such as to correct for .dy-

To this end'the potential source supplying .each control 60 can be advantageously associated with the electron beam scanning means including the deflection coils Mend 26 of Figure 1.

The electrostatic deflection plates .42 associated with each outer beam are provided for the purpose of deflecting the beam in a direction substantially perpendicular to the direction of deflection by the magnetic plates 4% In accordance with the invention, the plates 42 are made of non-magnetic material, and, for the purpose of achieving uniformity in the electrostatic field throughout the spaces between them, the plates are disposed substantially parallel to one another and to the plane into which the three beams are desired to be converged. Plates 42 are maintained at suitable relative potentials by one or more leads 64 connected through an electrostatic convergence control 66 to suitable sources of potential (not shown) to provide an electrostatic deflection field of the desired intensity. To effect both static and dynamic convergence, control 66 may be advantageously associated with the electron beam scanning means including deflection coils 24 and 26 of Figure 1. The leads 64- may be brought out of the tube at any convenient location such as the tube base 20. Mounting of the electrostatic deflection plates 42 may be accomplished in any desired manner such as for example by aflixing the plates to the transverse member'44 or any other convenient support structure. When both plates 42 are mounted on a common electrically conducting support such as the member 44 one of the plates 42 must be suitably electrically insulated from the support as by means of insulator 6%. For additional mechanical support the electrostatic deflection plates 42 are preferably attached, as by welding, to the corresponding magnetic deflection plates at their inner edges 56. Also the plates 42 may have outstanding portions '70 at their outer edges which may be secured, as by welding, to the pole pieces 54 of the magnetic plates 40 to enhance the structural strength and rigidity of the assembly. a

Thus it may be seen that the present'invention provides a beam deflection or convergence system for plural electron beam electron discharge devices in which sloping or .mutually inclined magnetic deflection plates and separate parallel. non-magnetic electrostatic deflection plates insure optimum linearity and independence of de- Patent of the United States is:

1. Electron beam deflection means for an electron discharge device comprising a pair of magnetic deflection plates straddling the path of the electron beam, said magnetic deflection plates having outturned flanges at one extremity thereof forming pole pieces adapted to magnetically couple to a source of magnetomotive force, the entire opposing surfaces of said magnetic deflection plates straddling the path of the electron beam being continuously, mutually, and angularly inclined to each other with the spacing of said opposing surfaces adjacent said one extremity greater than their spacing remote from said extremity, a pair of electrostatic deflection plates straddling the path of the electron beam between and in a common transverse plane with the pair of magnetic deflection plates, said electrostatic deflection plates being of non-magnetic material and having confronting surfaces substantially parallel to each other and to the path of the electron beam whereby an electrostatic field established therebetween will be-substantially uniform throughout the space .betwen said electrostatic deflection plates,

ally, and angularly inclined relative to each other with their spacing at saidone extremity greater than their spacing remote from said extremity, whereby the magnetic field induced between said magnetic deflection plates through coupling at said one extremity is substantially uniform throughout the space between the magnetic deflection plates, a pair of electrostatic deflection plates straddling the path of each electron beam between each respective pair of magnetic deflection plates, said electrostatic deflection plates being of non-magnetic material and being substantially parallel to each other and to the direction of beam deflection by the magnetic deflection plates, and means for applying a potential difference to said electrostatic deflection plates.

3. In an electron discharge device having means for generating a plurality of electron beams, a pair of magnetlc deflection plates of ferromagnetic material straddling the path of each beam, each pair of said magnetic deflection plates having magnetic pole pieces at one extremity thereof adapted to magnetically couple to a source of magnetomotive force, said magnetic deflection plates being each substantially parallel to the electron beam and having their entire opposing surfaces continuously, mutually, and angularly inclined relative to each other such that the magnetic field induced between said magnetic deflection plates of each pair is substantially uniform throughout the entire space between them, a pair of electrostatic deflection plates straddling the path of each electron beam between and in a common transverse plane with each respective pair of magnetic deflection plates, said electrostatic deflection plates being of non-magnetic material and being substantially parallel to each other and to the direction of beam deflection by the magnetic deflection plates, means securing each magnetic deflection plate to the respective adjacent electrostatic deflection plate, and means for applying a potential difference to said electrostatic deflection plates.

4. In combination with an electron discharge device having an envelope and means for generating within the envelope a plurality of separate electron beams having the same general direction, a pair of magnetic deflection plates of ferromagnetic material straddling the path of each electron beam on opposite sides of a common plane of convergence, said magnetic deflection plates having integral outstanding flanges forming magnetic pole pieces at the extremity thereof adjacent said envelope, respective magnets external to said envelope positioned to magnetically couple to the pole pieces of each respective pair of magnetic deflection plates, said magnetic deflection plates being each substantially parallel to the electron beam and having their entire opposing surfaces continuously, mutually, and angularly inclined to each other with their spacing adjacent said pole pieces greater than their spacing remote from said pole pieces, whereby the entire magnetic field induced between each pair of said magnetic deflection plates is substantially uniform throughout the space between them, a pair of electrostatic deflection plates straddling the path of each electron beam between and in a common transverse plane with each respective pair of magnetic deflection plates, said electrostatic deflection plates being of nonmagnetic material and being substantially parallel to each other and to the direction of beam deflection by the magnetic deflection plates, said electrostatic deflection plates having outstanding flanges at one extremity secured to the flanges on the respective magnetic deflection plates, means for applying a potential diiference to said electrostatic deflection plates, and means for scanning said electron beams in a raster.

References Cited in the file of this patent UNITED STATES PATENTS 2,212,640 Hogan Aug, 27, 1940 2,332,881 Woerner Oct. 26, 1943 2,348,853 Schlesinger May 16, 1944 2,711,493 Lawrence June 21, 1955 2,719,242 Friend Sept. 27, 1955 2,742,589 Goodrich Apr. 17, 1956 2,752,520 Morrell June 26, 1956 2,757,301 Jones July 31, 1956 2,769,110 Obert Oct. 30, 1956 2,849,647 Francken Aug. 26, 1958 

